Powderless etching bath additive

ABSTRACT

ETCHING BATH FOR ZINC AND MAGNESIUM AND ALLOYS BASED THEREON COMPRISING AN AQUEOUS SOLUTION CONTAINING AN ETCHING AMOUNT OF NITRIC ACID, AND A WATER-SOLUBLE OR DISPERSIBLE, ANIONIC, ALIPHATIC CARBOXYLIC ACID CONTAINING AT LEAST ONE HYDROPHOBIC HYDROCARBON GROUP WITH ABOUT 8 TO 24 CARBON ATOMS AND HAVING A SULFONATE GROUP DEPENDING FROM A CARBON ATOM IN SAID HYDROCARBON GROUP.

United States Patent 3,730,899 POWDERLESS ETCHING BATH ADDITIVE Harold J. Messerschmidt, .lr., Box 8M, RD. 1, Stockholm, N.J.; Karl Heyman, 10 Crestmont Road, Montclair, N.J.; and Bernadou W. Johnsen H, 110 E. 23rd St., Apt. 3, Paterson, NJ. No Drawing. Filed Sept. 24, 1971, Ser. No. 183,660 Int. Cl. B4411 3/02; (323g 1/26 US. Cl. 156-14 12 Claims ABSTRACT OF THE DISCLOSURE Etching bath for zinc and magnesium and alloys based thereon comprising an aqueous solution containing an etching amount of nitric acid, and a water-soluble or dispersible, anionic, aliphatic carboxylic acid containing at least one hydrophobic hydrocarbon group with about 8 to 24 carbon atoms and having a sulfonate group depending from a carbon atom in said hydrocarbon group.

This invention relates to powderless etching. It more particularly refers to an improved additive composition for use in powderless etching baths.

To make photoengraving plates, a fiat or cylindrical plate of an acid-soluble metal such as magnesium, zinc or one of their alloys, is coated with a light sensitive coating or enamel. This coated surface is exposed to light through a negative having an image thereon so as to produce an image on the coating. The exposed coated surface is then developed to form an acid-resistant coating corresponding to the image produced by the exposure. This coating may be further hardened by heating and the final acid-resistant image is called the resist. Subsequently, the image bearing surface of the plate is subjected to etching by an acid to remove the metal which is not under the resist and thus to produce the image in relief.

In carrying out this etching process, techniques are employed to reduce lateral etching which undercuts the resist and/ or the relief side walls, which undercutting may cause a weakening, distortion or complete loss of the image.

A common method which the art formerly used for minimizing lateral etching consisted of powdering the sides of the relief with an acid-resistant powder, but this was a difficult and time-consuming operation which had to be repeated a number of times during the etching of each plate.

In recent years so-called powderless etching has been introduced and expanded. In this technique the etching bath is so formulated that the non-resist portion of the plate can be removed without the need for powdering the side walls.

Powderless etching is now a well-known, widely practiced technique. It is used to etch photoengraving plates and other similar shaped articles. Zinc, magnesium and alloys based thereon are generally used as the photoengraving plate metals.

In the growth of this art, it has been discovered that etching baths made up of aqueous solutions of nitric acid and one or more surfactants are quite suitable for powderless etching of zinc and/ or magnesium. Many technological contributions have been made to this art, such as for example in US. Pats. 2,640,763; 2,640,764; and 2,640,766; according to which the aqueous nitric acid etching baths are modified by the incorporation therein of aliphatic acids, or esters of aliphatic acids with polyhydric aliphatic alcohols, or sulfonates of succinic acid diesters.

One characteristic of these etching baths is their tendency to permit localized defilming on relief side walls. This results in a chipped surface which, in aggravated situations, causes poor printing plates. Another problem 3,730,899 Patented May 1, 1973 stems from the inability of these same baths to quickly form a protective film in the initial stage of etching that will protect the resist from lateral etching beneath it. Further, as the etching action of the acid penetrates to greater depths, there is a problem of preventing lateral etching of relief side walls. Another problem of great importance is the capacity of the etching bath to produce proper depths of etch in all areas of a combination plate, i.e., a plate having both line and half tone image areas. This latter problem, for example, is most vexing because the use of filming additives which may be expected to increase or stabilize the filming tendency of the etching bath usually also results in the production of lesser depths of etch in half tone areas of combination plates. On the other hand, while the use of smaller amounts of the filming additives might be expected to provide deeper etching in halftone areas, such modifications also tend to cause excessive etching and undercutting in open line areas of the same plate. These problems are often sufliciently serious to make the poor products which results therefrom readily apparent to even the casual observer, particularly as evidenced by a chewed appearance of the plate.

Many attempts have been made to remedy the situation and to formulate etching baths which will give acceptable etching speeds and good quality production. Thus in more recent patents than those set forth above, newer and improved formulations have been disclosed, which employ a Water-immiscible organic liquid. Thus the modern etching bath technology is generally based on aqueous nitric acid, a water-immiscible organic liquid and a surfactant. These modern etching baths have reached a high degree of commercial success and are in wide use throughout the world. Unfortunately, these modern etching baths still have a problem in that they are ecologically undesirable. The water-immiscible organic liquid, which is generally a petroleum solvent, is a serious pollutant. It is therefore desirable to eliminate this component from etching bath compositions or at least to reduce the level thereof as much as possible.

The most commonly commercially used surfactant in the powderless etching art is a material which is usually referred to in the trade as sulfonated castor oil. This is a commercially available material which is chemically mis-named. The material referred to is actually a sulfated castor-oil, mainly the sulfate ester of n'cinoleic acid (the is the hydroxyl group of ricinoleic acid is esterified with sulfuric acid to add a sulfate group thereon). Other surfactants which have been recommended in the patent literature in combination with the water-immiscible organic liquid are sulfosuccinates, petroleum sulfonates, alkylaryl sulfonates, sulfated alcohols, sulfated fats and oils other than sulfated castor oil, phosphate esters, polyether non-ionic surfactants, and alkylaryl ether sulfonates.

It is therefore an important object of this invention to provide a novel etching bath for zinc or magnesium based shaped articles such as photoengraving plates.

It is another object of this invention to provide an improved etching bath having markedly improved filming capacity.

It is a further object of this invention to provide a novel additive for use in connection with aqueous nitric acid etching baths.

Other objects of this invention are to provide a novel etching bath capable of producing desired depths of etch in all kinds of image areas of combination plates, to porvide an etching bath capable of forming a stable protective film to prevent or retard lateral etching and chipping of relief side walls and a smooth, uniform side Wall permitting easy release from a matrix, besides having visual appeal.

A still further object of this invention is to provide an improved etching bath for producing name plates, metal patterns, templates and the like.

Other and additional objects will become apparent from a consideration of this entire specification including the claims thereof.

In accord with and fulfilling these objects, one important aspect of this invention resides in the use of a water-soluble or water-dispersible anionic aliphatic carboxylic acid or ester thereof containing at least one hydrophobic hydrocarbon group with about 8 to 24 carbon atoms attached to the carboxyl group and at least one sulfonate group attached to a carbon atom in said hydrophobic hydrocarbon group as the surfactant in an aqueous mineral acid etching bath.

The mineral acid of an etching bath is generally nitric acid, although mixtures of nitric acid and small quantities of sulfuric, hydrochloric or acetic acids can be beneficial. Suitable amounts of mineral acid range from about 30 to 300 grams per liter of bath with a preferred range from about 70 to 250 grams per liter of bath. A most preferred range is about 80 to 200 grams per liter of bath. The mineral acid components of the powderless etching bath of this invention is per se known.

The sulfonated carboxylic acids of this invention are true sulfonates as distinguished from the so called sulfonated oils like sulfonated caster oil which products are actually sulfates or esters of sulfuric acid. The true sulfonates of this invention differ from the sulfates by the fact that in the sulfonate, sulfur is directly linked to a carbon atom rather than through an intermediary oxygen atom as in the sulfate.

Examples of fatty acids which in their sulfonated condition are useful in this invention are for example caprylic, lauric, stearic, isostearic, behenic, lignoceric acids, undecylenic, oleic, linoleic, linolenic, eleo, stearic, arachidonic acids and the like. Saturated and unsaturated fatty acids which have substituents on their hydrocarbon chains can also be sulfonated to add a sulfonate substituent bonded to a carbon atom thereof. Examples of such acids are ricinoleic, 9,10-dihydroxystearic, -chloroor 9,10- dichlorostearic acids, beta-phenylpropionic, 10-phenylundecanoic and 9,10-dibenzylstearic acids. In many cases the esters, amides and nitriles, chlorides and/or anhydrides of these fatty acids can be sulfonated with ease, and the sulfonation products thus produced are applicable in this invention provided there is a sulfur-carbon bond an provided they hydrolyse in an aqueous acid etching baths into the corresponding sulfonated carboxylic acids. The sulfonated acids of this invention can be pure fatty acids or can be mixtures of fatty acids and/or esters or other derivates thereof such as occur naturally in vegetable, animal or marine oils, fats and waxes or in synthetic fatty acids derived from petroleum, bituminous coal and natural gas. Where mixtures of sulfonated fatty acids are to be used, sulfonation of the fatty acids can be accomplished before and after mixing.

The sulfonation of fatty carboxylic acids is a well established procedure and can be accomplished by different means as the occasion demands. Saturated fatty acids can be sulfonated directly in the alpha-position by reaction thereof with chlor-sulfonic acid or sulfur trioxide, which may be dissolved in sulphur dioxide, dioxane or chlorinated hydrocarbons. Alpha-sulfonations can also be accomplished less directly by the Strecker reaction of an alpha-bromo fatty acid with sodium sulfite. Side chain sulfonation of phenylalkanoic acids like 4-phenylcaproic, 10-phenylundecanoic, phenylstearic and 9,10-dibenzylstearic acids can be performed with a trioxane-sulfur trioxide complex. The same method is used for the alphasulfonation of hydroxystearic and 9,10-dihydroxystearic acid. Monoand polyunsaturated fatty acids having hydrocarbon chains in ther ange of 8 to 24 carbon atoms can be sulfonated with sulfur trioxide dissolved in sulfur dioxide to yield truly sulfonated carboxylic acids, e.g.

oleic acid yields predominately ll-sulfo-oleic and 9-hyhydroxy-lO-sulfostearic acids when reacted with a stoichiometric amount of sulfur trioxide. Truly sulfonated ricinoleic acid is obtained by sulfonation with acetyl sulfonic acid which is itself obtained by reacting sulfur trioxide with glacial acetic acid or acetic anhydride.

It is truly surprising that when a typical aqueous solution of nitric acid, in a concentration which is conventionally used for zinc or magnesium plate etching, is modified -by the admixture thereof with sulfonated fatty acid as set forth herein, the resultant composition is suitable for use as an etching bath with very little or no water-immiscible organic liquid required in the composition. Thus, in accord with this invention, etching baths are provided having the following composition:

Grams per liter Nitric acid, 300-3000 Sulfonated aliphatic acid l.O-15.0 Water-immiscible org. liquid 0.0-2.0 Water Balance In etching with the baths of the present invention it has been found to be desirable to impinge the bath against the surface to be etched, as by splashing. In theory, at least, the etching bath forms a partially acid-resistant film on the resist-free metal surfaces, and when the bath is impinged against the surface to be etched in a direction normal to that surface, the film is broken. On the other hand when the bath hits the sides of the relief, the film is generally not broken because of insufiicient striking force and etching of the sides (or under-cutting) is substantially reduced.

An etching machine of the type disclosed in Pat. No. 2,669.048, issued Feb. 16, 1954, and entitled Etching Machine can be used. In this machine elongated paddles dipping into the bath composition intermittently throw, by splashing, the etching bath composition in sheets upwardly against the image bearing side of the object being etched, e.g. a plate. Other types of etching machines known to the art are also applicable.

As used in this specification, the terms etch factor ratio (EFR) is defined as the ratio of (1) the depth of the etch adjacent to a line of resist divided by one half of the loss in width of metal immediately beneath the resist using a particular additive to (2) the depth of the etch adjacent to a line of resist divided by one half of the loss in width of metal immediately beneath the resist when only nitric acid is used in the exact concentration as was used with the particular additive:

EFR

Wn T where D11 is the etch depth with additive Dn is the etch depth without additive Wa is the under cutting loss with additive Wit is the under cutting loss without additive The following examples are given to illustrate the present invention, but are not to be construed as limiting thereon.

EXAMPLE I An etching bath was made up consisting of 8% by weight of 42 B. nitric acid, 0.45% by weight of 11- sulfo-oleic acid and the balance water. This bath was used to etch magnesium printing plates having a typical, representative resist image thereon. Etching was carried out for 3 minutes in a commercial paddle type etching machine of the type described in US. Pat. No. 2,669,048. The quality of the etched plates was good.

The etch factor ratio (EFR) was 11:1.

EXAMPLE 11 Example I was repeated but an identical weight of commercial sulfated castor oil was substituted for the sulfonated oleic acid. The result was a blanking out of the plate. No improvement was obtained by either decreasing or increasing the amounts of the sulfated castor oil used.

EXAMPLE III EXAMPLE IV Example II was repeated with the addition of 0.5% by weight of the heavy aromatic naphtha. This large amount "of naphtha was necessary in order to obtain a barely acceptable plate. Due to partial blanking out of the plate the EFR is not measurable.

EXAMPLE V Example IV was repeated using additions of 0.6% by weight of sulfated castor oil and 0.6% by weight of heavy aromatic naphtha. The resulting plate was acceptable. The etch factor ratio was 8:1.

EXAMPLE VI Example III was repeated using sulfated castor oil in place of the 11 sulfo oleic acid. No etching took place and the plate remained blanked out.

EXAMPLE VII An etching bath was made up by mixing dilute nitric acid and sulfocaprylic acid in the following proportions:

Grams Nitric acid, 100% 8.00 Sulfocaprylic acid 0.75

Water to 100.00 milliliters.

The bath was maintained at 38 C. while being constantly agitated. A paddle speed of 500 r.p.m. was used to etch the plate for 3 minutes. The relief portions of the plate were found to have good sidewall formation and an EFR of 6:1.

EXAMPLE VIII Example VII was repeated with the addition of 0.02% by weight of a heavy aromatic naphtha (HAN, Humble Oil Co.) to the etching bath. The etched magnesium plates had good quality and an EFR of 6: 1. Concentrations of HAN higher then 0.05% lead to plate degradation.

EXAMPLE IX An etching bath was made up by mixing dilute nitric acid and sulcfo behenic acid in the following proportions:

Grams Nitric acid, 100% 3.00 Sulfobehenic acid 0.02

Water to 100.00 milliliters.

Magnesium plates were etched in this bath at 38 C. for 8 minutes. The EFR was 3: 1.

What is claimed is:

1. An etching bath for photoengraving plates based on zinc, magnesium or alloys thereof comprising:

30.0 to 300.0 grams per liter of 100% nitric acid,

6 1.0 to 15.0 grams per liter of water-soluble or Waterdispersible sulfonated fatty acid having 8 to 24 carbon atoms in which the sulfur is bonded directly to a carbon atom,

00 to 2.0 grams per liter of a water-immiscible organic liquid, and

the balance water.

2. An etching bath as claimed in claim 1 wherein the acid moiety of said sulrfonated fatty acid is a member selected from the group consisting of caprylic, lauric, stearic, isostearic, behenic, lignoceric, undecylenic, oleic, linoleic linolenic, eleostearic, arachidonic, ricinoleic, 9,10- dihydroxystearic, 10-chlorostearic, 9,10-dichlorostearic, beta-phenylpropionic, 10-phenylundecanoic, and 9,10- dibenzylstearic.

3. An etching bath for photoengraving plates, based on magnesium or alloys thereof, which bath comprises:

30.0 to 300.0 grams of nitric acid per liter of bath;

1.0 to 15.0 grams of sulfo-oleic acid per liter of bath;

from 0.0 to 2.0 grams of a water-immiscible hydrocarbon or petroleum liquid per liter of bath; and

the balance water.

4. An etching bath as claimed in claim 3, wherein said sulfo-oleic acid comprises ll-sulfo-oleic acid and wherein said bath contains substantially no water-immiscible hydrocarbon or petroleum liquid.

5. An etching bath as claimed in claim 1 comprising water, nitric acid and sulfo-caprylic acid.

6. An etching bath as claimed in claim 1 comprising water, nitric acid, and sulfo-undecylenic acid.

7. An etching bath as claimed in claim 1 comprising water, nitric acid and sulfo-behenic acid.

8. An etching bath as claimed in claim 1 wherein the plates are based on magnesium or alloys thereof.

9. Method of etching a magnesium photoengraving plate comprising contacting the plate surface with an etching bath comprising:

30.0 to 300.0 grams of 100% bath;

1.0 to 15.0 grams per liter of water-soluble or waterdispersible sulfonated fatty acid having 8 to 24 carbon atoms in which the sulfur is bonded directly to a carbon atom; and

from 0.0 to 2.0 grams per liter of a water-immiscible organic liquid, said liquid being a hydrocarbon or petroleum solvent; and

the balance water.

10. Method as claimed in claim 9, wherein said sulfonated fatty acid is sulfo-oleic acid.

11. Method as claimed in claim 10, wherein said sulfooleic acid is substantially ll-sulrfo-oleic acid.

12. Method as claimed in claim 9, wherein said bath contains substantially no hydrocarbon or petroleum solvent.

nitric acid per liter of References Cited UNITED STATES PATENTS 1,828,194 3/1958 Hopkins et al. 15614 3,067,080 12/1962 Kaveggia et al 15620 3,234,137 2/1966 Lemaire et al 252 79.4 3,376,228 3/ 1968 Ruzicka 252-79.4 3,436,283 4/1969 Chrisley 156-44 JACOB H. STEINBERG, Primary Examiner U.S. Cl. X.R.

Disclaimer 3,730,899.Ha10ld J. Messerschmz'dt, J72, Stockholm, Karl Heymom, Mont- 

